1. Field of the Invention
This invention relates generally to improvements in infusion pumps such as those used for controlled delivery of medication to a patient. More specifically, this invention relates to improved methods and apparatuses for detecting occlusions in infusion pump systems.
2. Description of the Related Art
Infusion pump devices and systems are relatively well-known in the medical arts, for use in delivering or dispensing a prescribed medication such as insulin to a patient. In one form, such devices comprise a relatively compact pump housing adapted to receive a syringe or reservoir carrying a prescribed medication for administration to the patient through infusion tubing and an associated catheter or infusion set.
The infusion pump includes a small drive motor connected via a suitable transmission assembly for motor-driven advancement of a reservoir piston to administer the medication to the user. Programmable controls can operate the drive motor continuously or at periodic intervals to obtain a closely controlled and accurate delivery of the medication over an extended period of time. Such infusion pumps are utilized to administer insulin and other medications, with exemplary pump constructions being shown and described in U.S. Pat. Nos. 4,562,751; 4,678,408; 4,685,903; 5,080,653 and 5,097,122, which are incorporated by reference herein.
Infusion pumps of the general type described above have provided significant advantages and benefits with respect to accurate delivery of medication or other fluids over an extended period of time. The infusion pump can be designed to be extremely compact as well as water resistant, and may thus be adapted to be carried by the user, for example, by means of a belt clip. As a result, important medication can be delivered to the user with precision and in an automated manner, without significant restriction on the user""s mobility or life-style, including in some cases the ability to participate in water sports.
These pumps often incorporate drive systems which use lead screws or other transmission components coupled to motors. The motors can be of the DC, stepper, solenoid or other varieties. These drive systems typically provide an axial displacement of the syringe or reservoir piston thereby dispensing the medication to the user. Powered drive systems are advantageous since they can be electronically controlled to deliver a predetermined amount of medication by means well known in the art.
In the past, medication infusion pumps have included alarm systems designed to detect and indicate pump malfunction and/or nondelivery of the medication to the patient as a result of an occluded delivery line. Such alarm systems have typically used a high pressure limit switch for activating an alarm when the force applied to the reservoir piston plunger reaches a predetermined upper limit indicative of an occluded medication delivery line. In U.S. Pat. No. 4,562,751, the high pressure switch is positioned at one end of a rotatable lead screw, wherein the mechanical reaction force or backlash between the reservoir plunger and the pressure switch is proportional to the pressure applied to the medication as a result of attempted advancement of the reservoir plunger.
In actual practice, however, such high pressure limit switch systems have several disadvantages. For example, the lead screw must move axially some distance to actuate the switch. If the concentration of the medication requires very small (0.5 microliter) dosage increments, then the axial displacement of the reservoir plunger is designed to be very small per increment. Thus, several increments may be required to initiate an alarm when there is an occlusion. This elapse of several increments before an alarm is initiated may represent less medication delivered to the user than is desired. Moreover, there are frictional considerations. The lead screw mechanism of this pump design includes seals, a drive nut, a lead screw/motor coupling, and a bearing. All of these components have frictional properties. In systems where the high pressure switch is placed at the opposite end of the drive train from the reservoir plunger, the friction associated with these components are additive. These properties are known to change over time thereby making a fixed-setting, high pressure switch less effective.
There exists, therefore, a significant need for further improvements in medication infusion pumps, particularly with respect to providing an early warning of an occlusion or other pump drive system failures. The present invention fulfills this need and provides further related advantages.
To overcome the limitations in the prior art described above, preferred embodiments disclose a method and system for detecting occlusions or other pump system failures. Power is applied to a pump motor. A first pump motor current value is measured and a determination made whether the first pump motor current value exceeds a second value. If it does exceed the second value, the pump system is rewound at least to the point of reducing the pressure in the system and an alarm indication is given. A calculation is made of a total number of alarm indications, and a determination is made whether the total number of alarm indications exceeds a third value. If it does, a system error message is given.
In an alternative embodiment of the present invention, input power parameters are applied to a pump motor to provide a first pump cycle. A first encoder count is measured during the first pump cycle and a determination is made whether the first encoder count is less than a first value. If it is less than the first value, the fluid pump system is rewound at least to the point of reducing pressure in the system, and an alarm indication is provided. A calculation is made of a total number of alarm indications which is used to determine whether this exceeds a second value. If so, a system error message is provided. To provide system feedback, a determination is made whether the first encoder count is equal to a third value. If it is not equal to the third value, the input power parameters are adjusted to provide a second pump cycle which, in turn, causes a second encoder count of a different value than the first encoder count. The second encoder count will be greater than the first encoder count if the first encoder count was less than the third value. Alternatively, the second encoder count will be smaller than the first encoder count if the first encoder count was greater than the third value.
In still a further embodiment, an input power parameter is provided to a pump motor to provide a pump cycle. An encoder count is measured during the pump cycle. A torque value corresponding to the encoder count and to the input power parameter is determined. Another determination is made whether the torque value is greater than a first value. If so, the fluid pump system is rewound at least to the point of reducing pressure in the fluid pump system. An alarm indication is also provided. A calculation is made of a total number of alarm indications which is used to determine whether this total exceeds a second value. If so, a system error message is provided.